In particular, opening the contacts can lead to an electric arc, that is, sparking along with gas discharge. The appearance of arcs during the switching operation has negative effects on the contactor. The arc leads to the flow of electricity between the contacts continuing even after spatial separation of the contact surfaces in question, thus increasing the switching time. Furthermore, the electric discharge in the arc releases a relatively large amount of heat, which leads to undesirable heating up of the contactor. In particular, the heating causes a high wear (“burning off”) of the contacts, if the arc persists over an extended period at the point of the contacts. This eventually leads to the life of the contactor being reduced. In contactors with the so-called double break feature, an arc generally appears on both the contact pairs.
To solve the aforementioned problems, appropriate permanent magnets and arc quenchers are normally used in DC applications. The permanent magnets are arranged near the contact pairs. Each of them generates a magnetic field, which at an appropriate polarity generates a force on the respective arc, which is usually referred to as “magnetic blowout”.
This force will deflect the arcs in the direction of the arc quenchers arranged next to the contact pairs similar to quenching chambers.
For unidirectional operation, the permanent magnets can have the same polarity. In such an arrangement and when used properly, both arcs will be deflected one each into the two quenching chambers. However, if the contactor is connected with an incorrect polarity, both the arcs will be deflected by the blowout fields not into the quenching chambers, but in the correspondingly opposite direction, which could lead to them persisting for too long at a given point and thus giving rise to the aforementioned negative effects.
If the contactor needs to be operated bidirectionally, the permanent magnets usually have opposite polarities. Due to the current flow being in the opposite direction, both the arcs are thus deflected in the same direction. This ensures that irrespective of polarity, one arc is always deflected towards the quenching chamber, while the other is deflected away from the quenching chambers. Accordingly, appropriate measures also need to be taken here in order to prevent the negative effects caused by one of the arcs.
DE 10 2006 035 844 B4 describes a contactor for DC and AC operations, which, in addition to the two permanent magnets with opposite polarities, also comprises two blowout coils. The blowout coils are activated only if one of the arcs, deflected by the magnetic field of one of the permanent magnets, passes over to a suitably arranged baffle plate. Due to the effect of the coil's magnetic field, the arc is then guided in the direction of a quencher. The disadvantages in such an arrangement are the increased requirement of space for the additional quencher in the contacts, the heating caused by the current flow in the coil and last but not least, the increased manufacturing cost of the contactor due to additional coils being used.
DE 102 12 948 B4 describes a contactor for AC and DC operation, in which the contact bridge has a sharp-edged groove running transversely to the blow direction and located on the side away from the blow direction. If an arc is deflected away from the quenching chamber, the design of the groove prevents further deflection of the arc, which remains caught on the edge of the groove. When the direction of current flow is reversed in AC operation, the arc will only be deflected into one quenching chamber. The disadvantage here is that during DC operation, the arc in the aforementioned case remains in contact with the middle portion of the contact bridge for a relatively long time.